Writing Requires Listening
Ben Casnocha turned me onto this discussion about how both Paul Graham and Jason Fried place great importance on the ability to write well.
Being a writer, it warms my heart to see such importance being placed on writing. But I think that there is another, often overlooked reason why writing is such a necessary skill.
Good writers also understand their audience. Good writing doesn't exist in a vacuum. It is a product of understanding both your subject and your audience.
To write well, you must listen well and understand other points of view. That may be just as important as the ability to organize one's thoughts.
The ability to both read/listen and write/speak lets you close the communication loop, and persuade your audience of your point of view.